1. Field of the Invention
This invention relates in general to wellhead tree assemblies, and in particular to a non-orienting tree cap used to seal a christmas tree.
2. Description of the Prior Art
In the prior art, one type of wellhead assembly located of a subsea well includes a wellhead housing located at the upper end of a conductor pipe. One or more casing hangers for supporting the casing land in the wellhead housing. After the well has been drilled to total depth, tubing is installed, the drilling riser is removed and a Christmas tree is lowered onto and connected to the wellhead housing. Thereafter, a tree cap is placed on top of the Christmas tree in order to seal against the flow of subterranean oil and gas.
One type of tree has a production passage and an offset annular passage that communicates with a tubing annulus surrounding the tubing. In prior art systems, the tree cap would include a production bore mandrel and an annular passage mandrel to insert into the production and annulus bores to seal against leakage of subterranean oil and gas. The dual mandrel design requires orientation in order to correctly insert the tree cap onto the tree. Remotely operated vehicles (ROV) have been used to orient the tree cap; however, the task is not easy. The annular and production passages and tree cap mandrels are sensitive to damage, thus, it's important to avoid damaging them during orientation.